Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

499
FXUS63 KLOT 301123
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
623 AM CDT Tue Jun 30 2026

.KEY MESSAGES...

- Dangerous heat wave will likely continue into Thursday for
  most if not all of the area with daytimes highs in the 90s and
  peak afternoon heat indices of 100 to 110 degrees. Confidence
  across far northern IL is lower Thursday, due to potential
  effect of storms.

- Thunderstorm chances will begin to increase late in the week,
  likely bringing some heat relief for at least some areas.

- While likely not a complete wash out, there will be periodic
  chances for thunderstorm through the holiday weekend.

&&

.DISCUSSION...
Issued at 202 AM CDT Tue Jun 30 2026

Have elected to upgrade current advisory to an Extreme Heat
Warning, and extended headlines through Thursday based on the
potential for a fourth day of hot and humid conditions for much
of the area.

An upper level ridge, with H5 heights analyzed ~5960 meters,
was centered just south of the Ohio Valley across Kentucky and
Tennessee. This ridge is forecast to maintain its strength
across the area through at least Wednesday, before gradually
elongating west to east into the mid-Atlantic region late in the
week. Northwest of the ridge axis, low and mid-level
temperatures are progged to warm slightly today, with 925mb
temps in the +26/27C range and 700mb temps around +13C. This
will support surface temps a bit warmer than on Monday, with
mid-90s in many locations. Forecast soundings depict a
subsidence inversion in the 800-850mb range, limiting the mixing
depth despite otherwise breezy southwest low-level flow. This,
likely in combination with increasing crop evapotranspiration,
resulted in dew points somewhat higher than expected Monday,
especially across the southern half of the forecast area where
some upper 70s/80 degree dew points were observed even into the
late afternoon hours. Expecting similar trends again today,
supporting peak afternoon heat indices in the 105-110 range.
Latest guidance continues to indicate that mixing may be deeper
on Wednesday, potentially lowering dew points but also allowing
slightly warmer air temperatures - which would maintain similar
peak heat indices.

Most guidance then begins to shift the center of the upper
ridge off to the east across the Appalachians and mid-Atlantic
region by Thursday. Slight cooling of the mid-levels especially
into northwest and far northern IL and gradual southeastward
shift of the upper jet and storm track does suggest an
increasing threat of convection slipping into the northern parts
of the forecast area, especially by later Thursday afternoon
and evening. However, a good portion of the forecast area (or
perhaps the entire area if convection doesn`t materialize until
later or not at all) will likely see a fourth day of highs in
the low-mid 90s, mid-70s dew points and peak heat indices around
105. Based on this, and in collaboration with neighboring WFOs
will upgrade current advisory to an Excessive Heat Warning and
will extend all headlines through Thursday evening.

Global ensemble guidance continues to indicate that the upper
ridge will continue to deamplify Friday into the Independence
Day holiday weekend. Unfortunately, this results in what looks
to be a more active storm pattern for our region, as a zonal jet
pattern develops across the northern CONUS with indications of
several low-amplitude short waves transiting the flow. While
many dry hours are likely, at least periodic thunderstorm
potential will exist for the area through the weekend.

Ratzer

&&

.AVIATION /12Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 622 AM CDT Tue Jun 30 2026

SCT low-end MVFR stratocumulus developing over the area as of
TAF issuance may become BKN between 015 and 025 at times through
mid- morning as diurnal mixing lifts bases within a rather
moist low-level airmass. Otherwise, VFR conditions are expected
through the period.

SW winds will gust to around 20 knots through early afternoon,
though brief gusts as high as 25 knots are possible for the next
hour in response to mixing into a weakening low-level jet.
Winds will steadily increase with gusts over 25 knots mid to
late afternoon. Winds will diminish after sunset, with sporadic
gusts to near 20 knots persisting through the night and into
Wednesday morning. Though convection is expected to remain well
north of the area through the period, there is a 10 percent
chance outflow winds from convection over Wisconsin tonight
survive as far south as the Chicago terminals toward daybreak
Wednesday.

Kluber

&&

.CLIMATE...
Issued at 1249 AM CDT Tue Jun 30 2026

     .Daily Records for the Upcoming Week........

Chicago (KORD)
            Record High       Record Warm Minimum
June 30       99 (1953)            80 (2018)
July 1       103 (1956)            78 (1931)
July 2        99 (1970)            79 (1911)
July 3       102 (1949)            78 (1911)
July 4       102 (2012)            80 (1921)


Rockford (KRFD)
            Record High       Record Warm Minimum
June 30      102 (1931)            76 (2018)
July 1       101 (1931)            76 (1970)
July 2        99 (1910)            74 (1970)
July 3        99 (1925)            75 (2012)
July 4       102 (2012)            77 (1977)

NWS Chicago

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Extreme Heat Warning until midnight CDT Thursday night for
     ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-
     ILZ013-ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-
     ILZ103-ILZ104-ILZ105-ILZ106-ILZ107-ILZ108.

IN...Extreme Heat Warning until midnight CDT /1 AM EDT/ Thursday
     night for INZ001-INZ002-INZ010-INZ011-INZ019.

LM...Small Craft Advisory from 1 PM this afternoon to 9 PM CDT this
     evening for Winthrop Harbor IL to Gary IN.

&&

$$

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